Backspace is typically not one grapheme at a time, though it is for emoji. For scripts such as Arabic, it typically deletes ḥarakāt when they are composed on top of a base character. For a bit more discussion of how I hope to handle this in xi-editor, as well as links to the logic in Android, see https://github.com/google/xi-editor/issues/159
clarification: It is for some emoji, e.g. backspace on a family emoji will eliminate family members one by one. (on most browsers and platforms afaict). But flag emoji will be deleted as a group. IIRC handling of multicodepoint profession emoji is inconsistent.
